This invention relates to a sharpening device for the cutting knife of a face-to-face weaving machine, comprising a belt-shaped sharpening means provided with a sharpening face that is so disposable that the cutting knife during its movements comes into contact with this sharpening face, and that is movable in order to bring various areas of the sharpening face within reach of the cutting knife.
This invention also relates in particular to a face-to-face weaving machine provided with one or several such sharpening devices.
On face-to-face weaving machines two fabrics are woven one above the other, while pile warp threads are alternately interlaced in the top and in the bottom fabric. The pile warp threads, which connect both fabrics, are split on the weaving machine between the two fabrics, so that two separate pile fabrics are obtained. This occurs by means of a cutting device provided on the weaving machine.
This cutting device consists of a knife carriage onto which a cutting knife is attached. The knife carriage is movably disposed on a cutting bench extending according to the weft direction, and is moved back and forth on this cutting bench by means of a drive device, so that the pile warp threads are cut through by the cutting knife.
In order to obtain pile fabrics of an acceptable quality all pile warp threads must be cut through with a razor sharp cutting knife.
Because it is desired to have the cutting knife work uninterruptedly for a long time, while it nevertheless remains sufficiently sharp, it is known to provide a sharpening device on the weaving machine, with which the cutting knife can be sharpened during its back and forth going movements.
A known sharpening device is described in the French patent publication no. FR-2.556.638, and comprises two sharpening stones between which the cutting knife is moved at the end of the cutting bench. The sharpening stones are attached on elastic holders. At each extremity of the cutting bench such a sharpening device can be disposed.
There are two sharpening stone shapes in use. On the one hand there are the flat beam-shaped sharpening stones with a cambered sharpening face and on the other hand there are the round sharpening stones which have a conical sharpening face.
In the Belgian patent no. 899187 a sharpening device is described with which the sharpening can be interrupted in order to limit the wear of the cutting knife. In this device two beam-shaped sharpening stones with a curved sharpening face are provided, which are so disposed that the cutting knife moves between these sharpening stones and comes into contact with their respective sharpening faces.
In DE-GM-8412711 an elastic disposition for such sharpening stones is described.
In the Belgian patent no. 900272 a sharpening device is described with the characteristics mentioned in the first paragraph of this specification. This device comprises namely an elastically disposed round sharpening stone with a conical-shaped sharpening face, and is rotatable so that the cutting knife during rotation of the sharpening stone does not always come into contact in the same place with this sharpening stone.
In FR-2012734 a sharpening device with a belt-shaped endless sharpening means is described. By driving the sharpening belt in a circular movement various areas of the belt can be brought within reach of the cutting knife.
A number of disadvantages are however linked to these known sharpening devices.
In order to limit the wear and tear of the cutting knife the sharpening pressure may not be set high. On the other hand the sharpening pressure must be just sufficient in order to rub the abrasive grains of the sharpening face with every passage of the cutting knife against the edge of the knife.
When weaving, components of the yarn remain sticking to the cutting knife. With the sharpening movement these components are deposited on the sharpening face of the sharpening stones. The abrasive grains of the sharpening stones are embedded with these impurities so that the sharpening action is no longer efficient.
The weaving machine because of this weaves fabrics with a bad cut. Fabrics with a bad cut show pile stripes and shagginess. These disadvantages often lead to increased finishing costs of the pile fabric or result in the pile fabric having to be sold as a fabric of lesser quality, or even being no longer sellable. This is especially the case for velveteen or velvet with artificial and synthetic pile yarns.
The sharpening means of the known sharpening devices often have to be cleaned. This can only occur during standstill of the weaving machine with loss of production as inevitable result.
With the known sharpening devices the sharpening means after a certain standing time furthermore also exhibits a trace because of the fact that the abrasive grains come loose from their embedment. The sharpening surface is then no longer intact with a bad sharpening action as result. The sharpening means then has to be replaced, which again leads to a standstill of the weaving machine.
The purpose of this invention is to provide a sharpening device with which the disadvantages mentioned above are remedied.